Power transmission belts prepared from polyimide and polyketone elastomers

ABSTRACT

A polyimide having a repeating unit of the formula (I), (II), or (III): ##STR1## where LG is a linking group and W is an oligomeric chain selected from the group consisting of polyether, a polythioether, a polyetherthioether, polycarbonyl, or polysulfonyl, or a copolymer thereof.

This is a division of application Ser. No. 241,168, filed Sept. 2, 1988;now U.S. Pat. No. 4,959,444, issued Sept. 25, 1990.

BACKGROUND OF THE INVENTION

The present invention relates to temperature resistant thermoset plasticpolyimide, and polyketone elastomers and more particularly to thermallystable thermoset plastic polyimides, and polyketone elastomers useful inautomotive power transmission belts which are reaction injection molded.

The temperature requirements for engine accessory drive belts haveincreased so dramatically that conventional elastomers, used tofabricate power transmission belts, are not adequate for tomorrow'sautomobiles.

The obvious solution would be to incorporate new fabricating technologyand materials into a totally new method of manufacture for powertransmission belts. This is what led us to RIM processing, short forReaction Injection Molding. This is not to be confused with theInjection Molding process which is widely used today to makethermoplastic molded parts. The Thermoplastic Injection Molding machinesimply melts the plastic and injects it into a cold mold were it hardensand assumes the desired shape of the mold. These plastics can beprocessed over and over again by remelting, and injecting them into newmolds.

The RIM machine meters two chemically reactive liquids, commonlydesignated as "A" and "B" reactants, in a precise volumetric ratio to aimpingement mixer at near sonic velocity. The reacting liquid chemicalsare then injected into a low pressure mold before they have hadsufficient time to polymerize into a solid plastic. The resultingpolymer is a fully crosslinked thermoset plastic of enormous molecularweight that can never be reprocessed again, it will thermally degradebefore melting.

The key to the process is in the word "REACTION", i.e., (ChemicalReaction). The polymer is polymerized, created insitu, in the mold bythe spontaneous chemical reaction of two liquid oligomer systems witheach other. I use the term oligomer system because neither the A or Bside is a completely finished polymer. The A and B components areblended chemical intermediates which are liquid and have no chemicalreactive to themselves at the processing temperature. The two oligomerintermediates do, however, react very aggressively with each other uponmixing. Typical reaction times of 0.2 to 1 second are not uncommon.Finished, completely cured parts are commonly molded in 5 to 10 minutes.

Polymer technology has not kept pace with RIM technology. There a numberof RIM polyurea and polyurethane materials which satisfy the basicphysical characteristics required in these applications, namely, tensilestrength, flexural modulus, hardness, and elongation. In addition, theyhave superior dynamic properties over conventional millable gumelastomers such as Neoprene, Hycar, and Hypalon. They do not, however,have the temperature resistance necessary for automotive powertransmission belts.

Thermal degradation studies conducted on these elastomers clearly showthe thermally weak part to be the urethane or urea linkage. The polymerbackbone structures are capable of with standing much highertemperatures. The polythioether backbones are stable to about 600° F.,aliphatic polyethers are stable to about 670° F., and aromaticpolyethers are stable at temperatures in excess of 700° F. Oligomericdiamines used to formulate polyureas would satisfy all the requirementsfor power transmission belts if a more heat resistant chemical linkagecould be found. It would also satisfy all of the manufacturingrequirements if the new chemical linkage would form insitu by RIMprocessing. In accordance with the present invention, these oligomericprepolymers are terminated by a maleimide, citraconimide,triazolinedione, or vinylketone and the conventional linkages of thepolyurethane or polyurea have been replace by a much more stable linkageformed by Michael addition or Diels Alder reaction with these moieties.

Polymers formed by Michael (nucleophilic) addition of a bismaleimide areknown in the art. White, J. E. et al., "Reactions of Diaminoalkanes withBismaleimides: Synthesis of Some Unusual Polyimides," J. Appl. PolySci., 29, 891-99 (1984) discloses that polyimide elastomers can beobtained by reacting diaminoalkanes having flexible backbones withaliphatic and aromatic bismaleimides. Examples of the diaminoalkanes are1,8-diaminooctane, N,N-dimethyl-1,6-hexanediamine.

U.S. Pat. No. 3,741,942 to Crivello (1973) teaches a polyimide obtainedby reaction of a bismaleimide and a dithiol, however, these polyimides,while temperature resistant, do not have the other physical propertiesrequired for use in automotive power transmission belts and there is nodisclosure of RIM processing of the polyimides.

Bismaleimides have also been used to crosslink unsaturated rubbers asdescribed in U.S. Pat. No. 2,989,504 to Little (1961), and they havebeen reacted with diamines by Michael addition in making fibers andmolded articles as described in U.S. Pat. No. 2,818,405 to Kovacic(1957), U.S. Pat. No. 3,658,764 to Lyon (1972), U.S. Pat. No. 3,767,626to Bron (1973), and U.S. Pat. No. 3,878,172 to Bargain et al. (1975),and re No. 29,316 to Bargain et al. (1976).

U.S. Pat. No. 3,738,967 to Crivello (1973) teaches that polyimides canalso be prepared by a nucleophilic addition reaction of a bismaleimideand hydrogen sulfide. These polyimides are disclosed as being useful inmolding, insulation, and coating. Another class of polyimide is obtainedby reacting a bismaleimide with a diamine and then a sulfide or dithiolaccording to U.S. Pat. No. 3,766,138 to Crivello (1973).

SUMMARY OF THE INVENTION

A principal object of the present invention is to provide a thermallystable elastomer having the requisite performance characteristics foruse in power transmission belts.

Another object of the present invention is to provide a thermally stableelastomer which can be prepared and molded by reaction injectionmolding.

A further object of the present invention is to provide liquid oligomerswith bismaleimide, biscitraconimide, bistriazolinedione, orbisvinylketone terminations which are useful in reaction injectionmolding to provide thermally stable elastomeric articles.

A still further object of the present invention is to provide thermallystable power transmission belts which are prepared using the elastomersdescribed herein.

Another object of the present invention is to provide a reactioninjection moldable bismaleimide, biscitraconimide, bistriazolinedione,or bisvinylketone oligomeric prepolymer.

Another object of the present invention is to provide a process forreaction injection molding wherein the bismaleimide, biscitraconimide,bistriazolinedione, or bisvinylketone terminated prepolymers describedherein are reacted with a dinucleophile to prepare articles of thetemperature resistant elastomers described herein.

These and other objects are achieved in the present invention whichprovides:

A polyimide having one of the following repeating units in the formula.##STR2## where W is a member selected from the group consisting of apolyether, polythioether, polyetherthioether, polycarbonyl, or acopolymer thereof; and more particularly ##STR3## x is a carbon ornitrogen atom and when x is a carbon atom, one carbon atom may besubstituted by a methyl group;

m is 1 to 12 and preferably 4 to 12;

n is 1 to 5;

Where LG is a linking group and preferably a group of the formula:##STR4##

Where L represents a flexible linking group and more particularly agroup having one of the following structures: ##STR5##

Where u is 1 to 7 and preferably 1,3, or 7; t is 1 to 5 and preferably 1or 3; m is 1 to 12 preferably 4 to 12;

The linking group LG and L are usually divalent, however, trivalent andtetravalent linking groups such as ##STR6##

N,N,N',N',-tetrakis(3-etherpropyl)ethylenediamine are also possible.When the linking group is trivalent or tetravalent, the A component maycontain 3 or 4 bismaleimido or like groups. It is douhtful that thelatter linking groups would be used since it would be more expedient tointroduce crosslinking into the polymer by using a polyvalentdinucleophile.

W represents a oligomer of between 500 and 6,000 in molecular weight. Itcan be an aliphatic polyether, polythioether, polyetherthioether, or apoly-metaphenylether. W may also represent a co-polymer of two or moreof these moieties. When W is a branched chain moiety, there may be 2 to4 reactive terminal groups.

A bismaleimide, biscitraconimide, bistriazolinedione, and bisvinylketoneterminated oligomeric prepolymer with one of the following formula.##STR7##

A temperature resistant elastomer prepared by reacting a bismaleimide,biscitraconimide, bistriazolinedione, or bisvinylketone terminatedprepolymer of the formulas (V)-(VII) with a dinucleophile in a MichaelAddition or a Diels Alder Addition polymerization.

DETAILED DESCRIPTION OF THE INVENTION

Temperature resistant elastomeric polyimides in accordance with thepresent invention are prepared by reacting any of the prepolymers offormulas (V)-(VII) above with a dinucleophile in a Michael addition orDiels Alder reaction.

A particular advantage of the present invention is that the prepolymersof the formulas (V)-(VII) are useful in reaction injection molding.Hereinafter, the prepolymers of the formulas (V)-(VII) will be referredto as the "A component" and the dinucleophile will be referred to as the"B component".

In reaction injection molding, it is essential that both the A and Bcomponents be liquid under the RIM conditions and that one of thecomponents be a low molecular weight material with a high degree ofmolecular mobility. This is important for two reasons. If one reactantis not a low molecular weight reactant (for example, having a molecularweight less than 1200), the reaction does not proceed quickly. Molecularmobility on the part of at least one component is required for highreactivity. In addition, if both reactants have high molecular weights,a solid reaction product is obtained after only one or two additionreactions. Once a solid product is produced the reaction shuts downprematurely, as a result the polymer will have a poorly developed matrixand relatively low molecular weight. Accordingly, to achieve thereactivity and polymer properties desired in a RIM process, at least onereactant must have good molecular mobility, the reaction must reachcompletion, and the high molecular weight of the polymer must be theresult of the RIM reaction. It can not be achieved by using highmolecular weight, in excess of 6,000, A or B components.

In accordance with the present invention, two approaches have beenadopted with respect to the design of component A. Formula (V)represents bismaleimides, biscitraconimides and bistriazolinedioneswhich are liquid under the RIM reaction conditions. Due to the symmetryof these compounds, there is a tendency for the compounds to becrystalline solids. In accordance with the present invention, however,the compounds are designed with a flexible linking group L between themaleimide moieties which places a sufficient internuclear distancebetween the rings and provides sufficient flexibility to the moleculethat the compounds are liquid under the RIM reaction conditions.

In order to provide sufficient flexibility and internuclear distance inprepolymers of the formula (V), L is preferably an aromatic ether group,an aliphatic ether group or aromatic ether groups alternating with shortaliphatic chains. The aliphatic chains between ether linkages preferablyhaving 4 to 12 carbon atoms. The aromatic ether preferably includes ameta substituted phenylene as opposed to a para substituted phenylenebecause meta substitution provides substantially lower melting points inthe A component and much greater flexibility to the linking group.

A second approach to designing component A is to end cap a hightemperature resistant liquid prepolymer with a low molecular weightbismaleimide, biscitraconimide, bistriazolinedione or bisvinylketone.Prepolymers in accordance with this embodiment of the invention arerepresented by the formulas (VI) and (VII).

Selection of the dinucleophile or B component will depend to a largedegree on the nature of the A component. Where the A component is arelatively low molecular weight compound of the formula (V), highermolecular weight B component may be used in the RIM process. On theother hand, where the A reactant is a higher molecular weight prepolymerof the formula (VI) or (VII), a lower molecular weight dinucleophilewill be selected.

Dinucleophiles useful in providing thermoset elastomers by RIMprocessing can be more particularly represented by formulas ##STR8##

Where R is a hydrogen atom or a lower alkyl group (e.g., and alkyl groupcontaining 1 to 4 carbon atoms), and W is a polyether, aromatic oraliphatic, aliphatic polythioether, aliphatic polyetherthioether or aco-polymer of aromatic and aliphatic polyethers or polythioethers whichpreferably do not substantially degrade upon heating to temperatures ofat least 350° F. and more preferably at least 400° F. More particularlyW' can be represented by the formulas (X)-(XII).

    -R.sup.1 -(-O-R.sup.2 -S-R.sup.3 -).sub.x -                (X)

    -(-R.sup.1 -O-R.sup.2 -).sub.x -                           (XI)

    -(-R.sup.1 -S-R.sup.2 -).sub.x -                           (XII)

Here R¹, R², and R³ represent straight or branched chain alkylene orarylene groups 2 to 12 carbon atoms, x is a function of the totalmolecular weight divided by the molecular weight of the repeating units.The total molecular weight is most generaly between 500 and 6,000 and xis typically between 2 and 70. As a general rule, the dinucleophilesvary in reactivity as follows: aromatic primary amines greater thanaliphatic primary amines, primary amines greater than secondary amines.Mercaptans are very slow to react. Consequently, when they are used inthe RIM process, a tertiary amine such as quinuclidine ortriethyldiamine is added to the A component as a catalyst. Triethylaminemay also be used as a catalyst but it tends to be too volitile. All ofthe following dinucleophiles have been used for W'.

Representative examples of dinucleophiles are provided in the followingtable.

                                      TABLE                                       __________________________________________________________________________     1.                                                                              ##STR9##                                                                    2.                                                                              ##STR10##                                                                   3.                                                                              ##STR11##                                                                   4.                                                                              ##STR12##                                                                   5.                         JEFFAMINE T-5000 (Texaco Corp.)                      ##STR13##                [C.A.S. Registry No. 64852-22-8] Were x + y +                                 z = 27                                             6.                         JEFFAMINE D-Series (Texaco Corp.)                                             Product                                                                              X      Mol. Wt.                               ##STR14##                 D-230 D-400 D-2000 D-4000                                                            2-3 5-6 33 (Avg.) 68                                                                   230   400 2,000 4,000             7.                                                                             JEFFAMINE ED-Series (Texaco Corp.)                                             ##STR15##                                                                          Product                                                                            b               a + c                                                                             Mol. Wt.                                             ED-600                                                                              8.5            2.5   600                                                ED-900                                                                             15.5            2.5   900                                                ED-2001                                                                            40.5            2.5 2,000                                                ED-4000                                                                            86.0            2.5 4,000                                                ED-6000                                                                            131.5           2.5 6,000                                         8.                                                                             UNILINK 4200 (U. O. P. Corp.)                                                  ##STR16##                                                                   9.                                                                             UNILINK 4100 (U. O. P. Corp.)                                                  ##STR17##                                                                  10.                                                                             UNILINK XPA SERIES (U. O. P. Corp.)                                            ##STR18##                                                                             MATERIAL CODE      R.sub.1                                                                             R.sub.2                                              XPA-23             C'.sub.8                                                                            C'.sub.8                                             XPA-24             C.sub.8                                                                             C.sub.8                                              XPA-28             C.sub.6                                                                             C.sub.6                                              WHERE:                                                                                            ##STR19##                                                                     ##STR20##                                                                     ##STR21##                                        BIS-ANILINE M (Mitsui Petrochemicals)                                          ##STR22##                                                                    DYTEK ™ A (Du Pont)                                                         ##STR23##                                                                    BHMT (Du Pont)                                                                H.sub.2 NCH.sub.2 (CH.sub.2).sub.4 CH.sub.2 NHCH.sub.2 (CH.sub.2).sub.4       CH.sub.2 NH.sub.2                                                             bis-hexamethylenetriamine (BHMT)                                              C.sub.12 DIAMINE (Du Pont)                                                    H.sub.2 NCH.sub.2 (CH.sub.2).sub.10 CH.sub.2 NH.sub.2                         1,12-dodecanediamine                                                          DPTA (Du Pont)                                                                NH.sub.2 CH.sub.2 CH.sub.2 CH.sub.2 NHCH.sub.2 CH.sub.2 CH.sub.2              NH.sub.2                                                                      dipropylenetriamine (DPTA)                                                    TAPA (Du Pont)                                                                 ##STR24##                                                                    TAPED (Du Pont)                                                                ##STR25##                                                                  __________________________________________________________________________

W can also be formed from any of the polythioethers described in U.S.Pat. No. 4,366,307 to Singh et al. which is incorporated herein byreference.

These prepolymers react with dinucleophiles by a Michael addition orDiels Alder addition to afford the elastomers. For use in RIM processes,the prepolymer must be a free flowing liquid below 250° F. Preferably,this reaction proceeds under conditions compatible with the RIM process.

Typical RIM processing conditions vary because of the differences inproperties of the reactants and of the chemistry of the reactions, eachmaterial requires different processing conditions. Typical prepolymertemperatures ranged from 160° to 265° F. The higher temperatures, inexcess of 230° F., were avoided when ever possible for two reasons.First of all bismaleimides, biscitraconimides, bistriazolinediones, andbisvinylketones have a tendency to react with themselves. The higher thetemperature the more rapid the reaction, hence, shorter pot life. Thisis further aggravated by the high pumping pressure of the RIM injectors.The second reason involves the seals on the RIM machine, above 265° F.these seals begin to fail rapidly. Leaking material reduces injectionpressure and upsets the stoichiometric ratio between the two components.

Mixing ratio control is critically important. Because the RIM processdepends on a chemical reaction to achieve its finished properties, thestoichiometric ratio of the A component to the B component is importantto insure that all of the reactive sites have indeed reacted and thatyou have achieved the maximum possible polymer networking and molecularweight. This ratio is calculated by first calculating the equivalentweights of both the A component and the B component by dividing theirmolecular weights by: a average number of reactive sites per molecule.The actual component weight of component A in grams divided by theequivalent weight of component A equals the equivalence of component A.The equivalence of component A times the equivalent weight of componentB equals the actual weight of component B expressed in grams. The actualweights of both components A and B must be converted to volumetric unitsbefore they can be set on the RIM machine. This is done by dividing theactual weights of both components by their respective specificgravities. Very small changes can have catastrophic effects onproperties. For example, a 2% percent change in a preselected 1:1.2volumetric RIM ratio resulted in a 22% change in flexural modulus.

All currently available metering units measure the traveling speed ofthe piston and calculate the displaced volume flow rate of bothcomponents. It is necessary to record and control the volumetric flowrate ratio, to insure uniform polymer performance.

RIM injection pressures ranged between 2,000 and 3,500 psi. The typicalreaction time was 10 seconds, followed by an 8 hour post cure of 300° F.

The dinucleophilic B component and/or the A component may be a blend tocontrol the RIM reaction and the properties of the elastomer which isproduced. It was recognized early during our research that a blend ofdinucleophiles would be needed to realize all of the propertyrequirements for power transmission belts. The dinucleophiles wereselected on a temperature resistance and elastomeric tendency basis,i.e., a dinucleophile is selected which does not introduce thermallyunstable units, but does introduce flexible elastomeric units into thepolymer. Examples of dinucleophile blends (B side components) which haveproved to be useful in this invention are:

    ______________________________________                                        Jeffamine D-2000*     60%                                                     Jeffamine t-5000*     20%                                                     DuPont TAPED or TAPA**                                                                              10%                                                     Metsui Bis-aniline M***                                                                              5%                                                     U.O.P. UNILINK 4200****                                                                              5%                                                     Jeffamine D-2000*     80%                                                     DuPont TAPED**        15%                                                     1,3-bis(3-aminophenoxyl) benzene                                                                     5%                                                     Jeffamine t-5000*     80%                                                     DuPont TAPA**         10%                                                     Metsui Bis-aniline M***                                                                             10%                                                     ______________________________________                                          *A primary amine terminated aliphatic polyether available from Texaco.        **A primary amine terminated aliphatic chain available from DuPont.           ***A primary aromatic diamine available from Mitsui of Japan.                 ****A secondary aromatic diamine available from U.O.P. Corp.            

The Texaco Jeffamines are very long polyaliphaticether molecules whichmake up the bulk of the polymer. They are elastic, very flexible, andvery soft. The D series are diamines which promote linear chain growth,were as the T series is a triamine which promotes crosslinking betweenchains. The crosslinkages formed by the T series Jeffamine are, however,long branched chains of about 1,800 in molecular weight. Thiscrosslinkage does increase the resilience of the polymer but does notimprove the low tear resistance of the polymer.

To improve the tear resistance, molecules such as DuPont TAPA,tris(3-aminopropyl)amine, or TAPED, N,N,N',N',-tetrakis(3-aminopropyl)ethylenediamine are introduced, thesepolynucleophiles with short, low molecular weight aliphatic branchesproduce very tight crosslinkages in a honeycomb like polymer network. Itis this polymer networking that provides the resilience, tearresistance, and wear resistance to the polymer. The U.O.P. and Mitsuimaterials are hardness adjustors. They are short aromatic diamines withstiff para phenyl rings in there backbones.

It was also discovered that bismaleimides, biscitraconimides, andbisvinylketones could also be blended to control the rate, or kineticsof the RIM reaction. It also provided a convenient means to introducehard segments or tough segments into the polymer. Biscitraconimidesreact slower than bismaleimides with dinucleophiles and impart aresilience to the polymer because of its pendent methyl group.Bistriazolinediones and bisvinylketones react much more rapidly withdinucleophiles than bismaleimides and provide a means to increase therate of reaction and reduce the post cure time and temperature.Bisvinylketone linkages are not ring structures, therefor they are moreflexible than the maleimide, citraconimide, or triazolinedionestructures. Examples of the most useful bismaleimide, biscitraconimide,bistriazolinedione, and bisvinylketone used are: ##STR26##

The second approach is to end cap a liquid prepolymer with a lowmolecular weight bismaleimide. The theory being that the end cappinggroups, although high melting solids, are so small compared to the bodyof the molecule that they have little effect on the melting point of thetotal molecule. This proved to be true. The bismaleimides represented byformula (V) and more specificaly by formula (XVIII) above are examplesof the end capping bismaleimides used.

A number of liquid A components of the general formula (VI) were madefrom mercaptan terminated polythioethers and polyoxythioethers fromProducts Research & Chemical Corporation by the following method.

PROCEDURE: A solution containing (1.0 mole equivalent) of mercaptanterminated prepolymer, and 1 ml. of triethylamine in drydimethylformamide (DMF) was added drop wise to a mechanically stirredsolution of a bismaleimide (BMI) with the general formula (V) or morespecificaly formula (XVIII) (2.1 mole equivalent) in dry DMF containing10% of m-cresol, at 60° C. The mixture was stirred at that temperaturefor 24 hours, then poured into a 10 to 1 solution of methanol and aceticacid with vigorous stirring. The mixture of solvents were decanted andthe viscous polymer product was washed three times with methanol, thendried under reduced pressure. The bismaleimide end capped prepolymerthen could be reacted with low molecular dinucleophiles such as DuPontDYTEK A (2-methylpentamethylenediamine) blended with TAPA(tris(3-aminopropyl)amine) and/or TAPED (N,N,N',N',-tetrakis(3-aminopropyl)ethylenediamine). Examples of Products ResearchCorporation prepolymer blends are:

    ______________________________________                                               RW-2063-70                                                                             80%                                                                  RW-2064-70                                                                             20%                                                                  RW-2064-70                                                                             80%                                                                  RW-2065-70                                                                             20%                                                           ______________________________________                                    

RW-2063-70 is a mercaptan terminated polyoxythioether prepolymer with anaverage molecular weight of 6,500 and an average functionality of 2.75.

RW-2064-70 has the same general structure as RW-2063-70 differing onlyin the molecular weight 2,850 and the functionality 2.0.

RW-2065-00 is a short chain dimercaptan with a molecular weight of154.3, functionality of 2.0, and the formula HSCH₂ CH₂ SCH₂ CH₂ SH.

Typical nucleophiles (B components) used to produce elastomers byreaction with A components prepared by endcapping liquid prepolymerswere piperazine, 2-methylypiperazine, methylene dianiline, DuPont DPTA(dipropylenetriamine), TAPA (tris(3-aminopropyl)amine), TAPED(N,N,N',N',-tetrakis(3-aminopropyl)ethylenediamine),Cis-diaminocyclohexane and 1,12-dodecanediamine. This second method wasused considerably during the early polymer evaluation stuides because itwas something we could do quickly to obtain polymer samples.

Another useful class of dinucleophiles is biscyclopentadienyl alkanesand, more particularly cyclopentadienyl alkanes having 1 to 15 carbonatoms in the alkylene bridge between the cyclopentadienyl rings. Thepreparation of these compounds is illustrated in ##STR27##

These compounds react with bismaleimide, biscitraconimide, andbistriazolinedione terminated prepolymers in a Diels Alder addition withthe formation of a polynorbornene elastomer. The basic reaction schemeis shown below. ##STR28##

The prepolymers of the present invention can also be reacted withbiscyclopentadienones to produce a RIM processable polyhydrophthalimide.This reaction is shown below. ##STR29## Where: Ph=phenyl C₆ H₅

L=represents a flexible linking group having one of the followingstructures. ##STR30## Where u is 1 to 7 and preferably 1,3, or 7 and

t is 1 to 5 and preferably 1 or 3.

The linking group L is usually a divalent, however, trivalent andtetravalent linking groups such as ##STR31##

N,N,N',N',-tetrakis(3-etherpropyl)ethylenediamine are also possible.

This reaction is desirable because it proceeds with the loss of carbonmonoxide which makes the reaction irreversible. ##STR32## Where: L₂=represents a flexible linking group of the same group of structures asL on page 24.

Ph=represents a phenyl group.

Compounds of the formula (XXIII) can be prepared as illustrated insynthesis Example 5.

For use in power transmission belts, the elastomers of the presentinvention must have the tensile, resiliency, solvent resistance andflexural characteristics which provide good service life as well as hightemperature resistance. Elastomers which are particularly preferred inthese applications have the following properties.

    ______________________________________                                        Tensile (kpsi)     1.5 to 3.5                                                 Elongation (%)     150 to 300                                                 Flexural Modulus (kpsi)                                                                          10.0 to 30.0                                               Shore hardness     75A to 45D                                                 Degradation temp. (in air)                                                                       > = 600° F.                                         ______________________________________                                    

RIM is the reaction of two highly reactive components insitu in a mold.In accordance with the present invention, the bismaleimide,biscitraconimide, bistriazolinedione, or bisvinylketone and thedinucleophile are impingement mixed and injected into a mold in aconventional manner where they react to form the thermally stableelastomers of the present invention.

The invention is illustrated in more detail by way of the followingnon-limiting examples.

SYNTHESIS EXAMPLE 1 Endcapping of Dimercaptans

Dimercaptodiethylsulfide (7.7 gr. or 0.1 mole equivalence) containing afew drops of triethylamine was added drop wise to a solution of (40.0gr. or 0.22 mole equivalence) of N,N',-bismaleimidodiphenyl methane,Matrimide 5258 available from Ciba Giegy Corp., in 500 ml. of freshlydistilled m-cresol. The mixture was stirred at room temperature for 2hours, then warmed to 60° C. A solution of (303.7 gr. or 0.213 moleequivalence) of RW-2064-70, a mercaptan terminated polythioetherprepolymer available from Products Research Corp., in 500 ml. m-cresolwas added slowly to the mixture and the resulting mixture wasmechanically stirred for 20 to 24 hours at 60° to 70° C., then for anadditional 2 hours 100° C. The mixture was cooled to 80° C. and (37.8gr. or 0.21 mole equivalence) of 1,1'-methylene di 1,4-phenylenebis-maleimide was added, then stirred overnight. The resulting mixturewas poured into a solution of methanol containing 10% acetic acid in astainless steel Waring blender and the viscous polymeric material wasbroken to form a resinous liquid polymer, separated in a separatoryfunnel from the methanol, the prepolymer was washed three times withmethanol, and dried in a rotoevaporator under vacuum at 60° C. for 3hours.

SYNTHESIS EXAMPLE 2 Endcaping of Dimercaptans

A solution of 0.1 mole equivalent of a mercaptan terminated liquidpolymer RW-2066-70, available from Products Research Corp., in 1 literdry DMF was added dropwise to a mechanically stirred solution of4,4'-bismaleimidocumyl metabenzene, available from Metsui PetrochemicalsCorp., (2.1 mole equiv.) in dry DMF, containing 10% of m-cresol and 1ml. of triethylamine, at 60° C.

The mixture was stirred at that temperature for 24 hours, then pouredinto a 10 to 1 solution of methanol and acetic acid with vigorousstirring: The solvents were decanted from the viscous prepolymer productand washed three times with methanol, then dried in a rotorevaporatorunder vacuum at 60° C. for 4 hours. ##STR33## Where: j=1, 2, 3, 4 andsometimes 6

k=38 to 91

The resulting bismaleimide endcapped prepolymer was reacted with variousdiamines such as DuPont C₁₂ DIAMINE, 1,12-dodecanediamine, or DuPontTAPA, tris(3-aminopropyl)amine, or 2-methyl piperazine to yieldamorphorous dark brown to light amber thermoset plastic resins.

SYNTHESIS EXAMPLE 3 Preparation of polyether diamines

In a 500 ml. round bottom three neck flask out fitted with a refluxingcondenser, mechanical stirrer, and addition separatory funnel was added150 ml. DMAC, 15.19 gr. of potassium carbonate, and 32.18 gr. of metachloroaniline. This mixture was stirred and heated to 150° C. After themixture had a chance to stabilize at 150° C. for 30 minutes 12.43 gr. ofhexanediol was added drop wise to the flask over a 1 hour period. Theflask was allowed to reflux overnight or 18 hours. The flask was thenallowed to cool down to room temperature. The contents were filter andthe solid potassium carbonate was discarded. The filtrate was then mixedwith water and 100 ml. of chloroform. The chloroform diamine layer waswashed with water 4 times. The organic layer was then distilled undervacuum. The chloroform and water fractions were discarded, the lastfraction was saved. The reaction yield was 83.0% of 6,6'-diaminom-phenoxyhexane. This nucleophilic aromatic substitution reaction wasused to make a variety of aromatic and aromatic aliphatic etherdiamines. ##STR34##

SYNTHESIS EXAMPLE 4 Preparation of liquid bisamleimides

To a vigorously stirred solution of 6,6'-diamino m-phenoxyhexane (0.1mole) in acetone under a nitrogen atmosphere, maleic anhydride (0.22mole) was added, the temperature outside being maintained at a constant20° C. The pale yellow solid of bis-maleamic acid soon obtained onaddition of maleic anhydride, was vigorously stirred for a further 0.5hour to complete the reaction. To the continuously stirred suspension ofcompound in acetone were added acetic anhydride (70 ml., excess) andfused sodium acetate (5 to 6 gr.), and the acetone was allowed toreflux. Refluxing and stirring were continued until the solution becameclear (2 to 2.5 hours).

The clear brownish yellow solution was poured into ice water and 100 ml.of chloroform was added and the whole thing was shaken in a separatoryfunnel. The organic layer was washed with water containing sodiumbicarbonate 4 times by shaking it in a separatory funnel. The organiclayer was then passed through a filtration chromatography columncontaining silica gel. The chloroform was the removed by distillationunder vacuum in a rotoevaporator. The resulting 6,6'-bismaleimidom-phenoxyhexane is a yellowish orange viscous liquid at roomtemperature. ##STR35##

SYNTHESIS EXAMPLE 5 Preparation of the biscyclopentadiene

A mixture of meta-dibromobenzene (1 mole), triphenyl phosphine (20 gr.),copper iodide (3 gr.), and palladium (II) acetate (1 gr.), in 1 liter ofdry triethylamine is heated and stirred at 100° C. Phenylacetylene (2.5moles), is added slowly and the resulting mixture is refluxed for 8hours. The mixture is cooled and the solid product washed with ether,then with water, and methanol. The product I, is then air-dried and usedin the next step. ##STR36##

Step 2

A mixture of potassium permanganate (3 mole),1,4-bis(phenylethynyl)arene, product I (1 mole), water (6 liters),methylene chloride (5 liters), acetic acid (400 ml.), and phase transferagent (Adogen 464 methyltrialkyl (C₈ -C₁₀)-ammonium chloride availablefrom Aldrich Chemical Co.) is mechanically stirred and refluxed for 6hours. After cooling, sodium-hydrogensulfite (20 gr.) is added slowly toreduce any unreacted permanganate. After 15 minutes the solution isacidified with 1 liter of concentrated hydrochloric acid and theprecipitated manganese dioxide is reduced by addition of excessconcentrated sodium hydrogensulfite solution. The aqueous phase isseparated and extracted with dichloromethane (3 liters). The combinedorganic layer is washed with 5% sodium hydroxide solution, driedmagnesium sulfate, filtered, and concentrated to give the product II.##STR37##

Step 3

A one mole equivalent sample of product II and two mole equivalent ofdibenzylketone is heated for 4 hours in a mechanically stirreddichlorobenzene solution. The mixture is diluted with addition of hexaneand the solid product is filtered, washed with hexane and dried.Purification of this product may be carried out by recrystallizationfrom acetone or methyl ethyl ketone. ##STR38## where: Ph=phenyl rings

SYNTHESIS EXAMPLE 6 Preparation of biscyclopentadienyl alkane

To a solution of sodium cyclopentadienyl (2 mole equivalence), in drytetrahydrofuran (THF) under nitrogen atmosphere and ice bathtemperature, is added drop wise a solution of 1,6-dibromohexane,selected from those with the general form shown below, (1 moleequivalence), in dry THF. When the addition is complete, the mixture isstirred at 5° to 10° C. for 6 to 12 hours. The resulting solution ispoured into an ice-cold dilute hydrochloric acid (5%) and the product isisolated by filtration or extraction. ##STR39## Where: X=Cl, Br, or Iand preferably Cl or Br ##STR40## Where: n=1 to 15

m=1 to 6

SYNTHESIS EXAMPLE 7 Preparation of activated bisvinylketone

To a solution of suberoyl chloride, ClCO(CH₂)₆ COCl, (1 moleequivalence) and aluminum chloride (2.2 mole equivalence) in methylenechloride at 0° C., is added drop wise a solution of trimethylvinylsilane (2.4 mole equivalence) in methylene chloride. The mixture isstirred at 0° to 5° C. for 6 to 10 hours, then poured in ice-cold 10%hydrochloric acid. The mixture is shaken in a separatory funnel,methylene chloride layer is washed with water, dried (MgSO4). Thesolution is then filtered and the methylene chloride is distilled undervacuum in a rotoevaporator at 50° C. to give bisvinylketone product.##STR41##

Having described the invention in detail and by reference to specificembodiments thereof, it will be apparent that numerous modifications arepossible without departing from the spirit of the invention as definedin the following claims.

What is claimed is:
 1. A power transmission belt prepared from aPolyimide having a repeating unit of the formula (I), (II), (III) or(IV): ##STR42## where LG is a linking group,W is an oligomeric chainselected from the group consisting of a polyether, a polythioether, apolyetherthioether, a polycarbonyl, a polysulfonyl, and copolymersthereof, and X is a carbon atom or a nitrogen atom and when X is acarbon atom, one carbon atom may be substituted by a methyl group. 2.The power transmission belt of claim 1 wherein LG is a group of theformula: ##STR43## where L represents a flexible linking group.
 3. Thepower transmission belt of claim 2 wherein L is selected from the groupconsisting of: ##STR44## where u is 1 to 7,t is 1 to 5, and m is 1 to12.
 4. The power transmission belt of claim 3 wherein W is representedby the formula ##STR45## where R is a hydrogen atom or a lower alkylgroup, andW is a straight or branched chain polyether, polythioether, orpolyetherthioether.
 5. The power transmission belt of claim 4 wherein Wincludes a repeating unit selected from the group consisting of:##STR46## where R₁, R₂, and R₃ may be the same or different andrepresent a straight or branched chain alkylene group having 2 to 12carbon atoms, an m-phenylene group or a p-phenylene group.
 6. The powertransmission belt of claim 4 wherein W is represented by the formula:##STR47## or the formula: ##STR48## where x is 2 to 80 and R, R₁, R₂, R₃may be the same or different and represent a straight or branched chainalkylene group having 2 to 12 carbon atoms, an m-phenylene group or ap-phenylene group.
 7. The power transmission belt of claim 3 wherein Wis ##STR49## m is 1 to 12; and n is 1 to
 5. 8. The power transmissionbelt of claim 1 wherein said polyimide is characterized by a tensilestrength of about 1.5 to 3.5 kpsi.
 9. The power transmission belt ofclaim 1 wherein said polyimide is characterized by an elongation ofabout 150 to 300%.
 10. The power transmission belt of claim 1 whereinsaid polyimide is characterized by a flexural modulus of about 10 to 30kpsi.
 11. The power transmission belt of claim 1 wherein said polyimideis characterized by a shore hardness of 75A to 45D.
 12. The powertransmission belt of claim 1 wherein said polyimide is characterized bya degradation temperature in air greater than 600° F.
 13. The powertransmission belt of claim 1 wherein said polyimide is represented ofthe formula (I).
 14. The power transmission belt of claim 1 wherein saidbelt is prepared by reaction injection molding.
 15. The powertransmission belt of claim 14 wherein said belt is prepared by reactioninjection molding a prepolymer of the formula ##STR50## where LG is alinking group,W is an oligomeric chain selected from the groupconsisting of a polyether, a polythioether, a polyetherthioether, apolycarbonyl, a polysulfonyl, and copolymers thereof and X is a carbonatom or a nitrogen atom and when X is a carbon atom, one carbon atom maybe substituted by a methyl group.
 16. The power transmission belt ofclaim 15 wherein said prepolymer is reacted with a polyamine.